Automatic apparatus for performing tests known by the name of ELISA and similar tests perform the tests on supports having a plurality of cells or wells for facilitating parallel and orderly processing of the samples. These supports which are known as micro-titer plates, usually have a format of 8 by 12 wells and can sometimes be divided into strips of 8 or 12 wells which in turn can sometimes be divided into individual wells. These wells, which are moulded in plastics, usually carry a dried reagent bound to the walls or bottom in what is known as a solid phase. The various steps of the test are performed thereon and are generally:
1. Sampling and dilution of the samples, calibrations and checks on the wells of the plates. The dilutions require a specific diluent. PA1 2. Incubation of the plate at controlled temperature with or without agitation for controlled periods of time (typically between 15 and 45 minutes, depending on the test). PA1 3. Washing of the wells with a specific washing solution. This is usually performed by dosing the washing solution into the wells and subsequently emptying them. PA1 4. Addition of various reagents (typically a specific, so-called conjugate test reagent, a chromogenic substrate, or a solution for stopping the chromogenic reaction). PA1 5. Steps 2, 3 and 4 may be combined and repeated in various ways according to the type of test performed. PA1 6. Photometric reading of the final reaction by various methods, one or several values being assigned to each cell. PA1 7. Calculations, presentation and storage of the results corresponding to each sample.
It is important to keep the incubation times approximately equal for all of the wells so that operations which take place cell by cell and not with the whole plate at the same time must be performed within a relatively short time.
Although the micro-titer plates are similar to one another, they have slight differences, particularly in their external shape and size, which complicates their handling when an undifferentiated use of any type is required.
However, all currently-known apparatus for performing laboratory tests of the ELISA type have the disadvantage of poor efficiency in performing the tests, particularly owing to the need to perform a complete test on a certain sample-holder plate before the machine can receive further plates of samples in order to perform further sets of tests.